The present invention relates generally to moving platform fluid systems and more specifically to a method and device to contain and distribute leakage from aircraft mounted fluid systems.
Modern aircraft require a variety of flammable fluids be transported between fluid storage areas and use locations. Typical examples include fluid piping between fuel tanks and engines, between hydraulic storage tanks and hydraulically operated equipment, and between lubricating oil storage areas and mechanical equipment. Fluid transport is typically through systems of piping, tubing or hoses, hereafter referred to in general as fluid lines.
Fluid leakage from flammable fluid lines which impinges other piping, wire bundles or structures is undesirable. Flammable fluid leakage adjacent a heat or ignition source is particularly undesirable for the obvious reason of aircraft safety. To contain fluid leakage, aircraft designers apply several methods, including sealing compartments through which fluid lines traverse or applying various designs of fluid line enclosures.
One current method to seal compartments involves the complex steps of applying sealing compounds during and after assembly, and installing a network of dedicated drains from each fluid trap (e.g., low point) region to avoid formation of puddles. Multiple low points within the compartment which for functional reasons cannot all be drained are often filled with a leveling compound to permit the drain network to function properly. Each seal and drain network requires confirmation via water test on every unit built.
One drawback of this approach is that all other piping, electrical wiring and structure within the compartment is exposed to any fluids that leak. Due to the chance of a leaking fluid line spraying fluid onto wire bundles, extraordinary effort is applied to the design, fabrication, and installation of wire bundles to prevent fluids from running along wires and contacting connectors. Further drawbacks include additional weight, increased labor hours during assembly to apply sealant and leveling compound, and additional time and labor to verify the quality of applied seals. The current methods also place a burden on the aircraft operators to restore the integrity of seals following maintenance actions. Also, when used, leveling compound hides the structure on which it rests, complicating or preventing visual inspection of that structure.
To prevent fluid leakage from wetting surrounding items, aircraft designers apply several designs of fluid line shrouds. Common shroud designs apply a tube or metal shroud surrounding the circumference of installed fluid piping and are used to capture and redirect flammable fluid leakage in areas including the space between flammable fluid leakage zones on the propulsion strut(s) and inside the fuselage of commercial aircraft.
An exemplary shroud design uses a dedicated sheet metal structure to surround propulsion strut fluid lines transitioning from one leakage zone to another. The sheet metal shroud comprises 2 halves assembled around the installed fluid lines, using clamp blocks and removable fasteners. The shroud halves overlap on assembly and a fillet seal is applied. The ends of the shroud are open to drain leakage into an adjacent leakage zone. Openings are provided in the clamp blocks to permit leaked fluids to flow past. Once leaked fluid exits the shroud assembly, it flows across strut structure to exit via a leakage zone drain system.
Another common propulsion strut shroud design advantageously uses a box-beam structure provided for other purposes. This structure is formed as a xe2x80x9cUxe2x80x9d channel. Fluid line support brackets are attached to the inside floor of the channel. Cover plates are then installed with gaskets and the forward end of the structure is sealed. Any fluid leakage flows aft onto the strut structure before exiting via a leakage zone drain system.
A further exemplary application of a common shroud design is applied over fuel line hoses supplying an auxiliary power unit (APU). The APU is frequently located in the aft end of an aircraft fuselage. The APU required fuel is delivered from the aircraft fuel system near the wing to the rear of the fuselage. To contain leakage, the APU fuel feed line is placed within a tubular shroud. The shroud is assembled from tubing and includes a dedicated drain system to purge it of any leaked fluids. The shroud is first installed between fuel supply and APU use points. The APU fuel feed line hose is then inserted within the shroud, and is supported on a shroud inner surface.
The disadvantages of common shroud designs are the lack of a firewall structure at a flammable containment end of the shroud, the general lack of dedicated drains to discharge leakage outside the aircraft rather than into another compartment or onto adjacent structure, and the inability to apply the design in a modular concept, wherein the fluid lines are preassembled within the shroud and the entire shroud assembly is installed or removed as a unit.
It is therefore desirable to provide a shroud design which overcomes the drawbacks and disadvantages of known shrouds and eliminates the need for compartmental sealing and leveling.
According to a preferred embodiment of the present invention, a shroud body internally supports one or more flammable fluid lines and associated support hardware. The combination of the shroud body, fluid lines and support hardware forms a shroud module. The shroud module can be removed/replaced as a unit if a fluid line leaks. The fluid lines are internally supported as an integral unit of fluid lines, allowing for any fluid leakage to traverse the shroud module and discharge through a drain connection disposed at both ends of the module. Shroud body supports are provided on the shroud module. The body supports are designed at a frequency to provide proper support of the shroud module and eliminate shroud body penetrations which create a potential leak path.
According to one preferred embodiment of the invention, the shroud module is installed as a unit on the propulsion strut structure of an aircraft. Each shroud module fluid line includes mechanical connections for connection to aircraft systems. All fluid connections within the shroud module are preassembled, and the shroud module is sealed before installation in the aircraft. At one sealed boundary end, the shroud module incorporates a fire-resistant, thick walled plate forming part of a firewall boundary of an aircraft. The firewall plate and its associated transition region are integrally formed. Fire-resistant tubing/piping connections are provided at the exterior, firewall boundary. Aircraft fluid lines are disconnected at these external connections to remove the module. The opposite, i.e., vapor barrier end of the shroud module is preferably provided as a thin-walled plate forming a shroud module fluid tight seal. System fluid lines at the vapor barrier end are provided with mechanical joints or terminate adjacent to the shroud, allowing shroud module removal/replacement.
In one preferred embodiment, a shroud module of the present invention comprises two major elements, a lower body and an upper cover. The lower body is formed as a generally U-shaped channel having an outwardly extending peripheral flange. The upper cover of the shroud module also has an outwardly extending peripheral flange, mating with the lower body peripheral flange to form a fluid-tight seal around the periphery of the shroud module. The lower body also includes an integral firewall, drain connections, and discrete attachment elements for installing the assembled shroud module to aircraft structure. The fluid lines and supporting clamp blocks are installed prior to upper cover assembly onto the lower body. The upper cover and lower body are preferably assembled with mechanical fasteners (with application of sealant and/or gasket materials), or by welding the flanged joint.
Fluid lines are disposed within the shroud lower body via spaced, elastomeric support blocks which, after installation, provide structural support, restraint, and physical separation between each fluid line. The support blocks are configured to allow any fluid leakage within the shroud module to flow to the drain connections. The support blocks are located at a frequency within the shroud module to provide proper support for the smallest diameter tube or pipe disposed in the module.
The shroud module of the present invention is configurable to support different aircraft engine designs requiring different firewall boundaries. The shroud module is preferably formed as a two-piece assembly, but can also be a multi-piece component. In an exemplary application, the shroud module is supported as a unit from aircraft structure such as the propulsion strut. With the exception of the firewall and its associated transition region, the shroud is preferably formed of a thin-wall, lightweight material.
Further areas of applicability of the present invention will become apparent from the detailed description provided hereinafter. It should be understood that the detailed description and specific examples, while indicating the preferred embodiment of the invention, are intended for purposes of illustration only and are not intended to limit the scope of the invention.